Apple has released an absolutely massive 94 page, 1.8MB PDF detailing what appears to be every single possible chip, port, slot, bus, fan, drive, component, and mechanism put into Appleis new machine. An excerpt from the PDF:

This developer note describes the all new 64-bit Power Mac G5 computer. The note provides information about the internal design of the computer, its input-output and expansion capabilities, and issues affecting compatibility.

This developer note is intended to help hardware and software developers design products that are compatible with the Macintosh products described here. If you are not already familiar with Macintosh computers or if you would simply like additional technical information, refer to Appendix A, "Supplemental Reference Documents" (page 77), for additional information.

[...]

The information is arranged in four chapters and two appendixes:

Chapter 1, "Introduction" (page 11), gives a summary of the features of the Power Mac G5 computer, describes the physical appearance of the enclosure, and lists compatibility issues of interest to developers.

Chapter 2, "Architecture" (page 21), describes the internal organization of the computer. It includes a functional block diagram and descriptions of the main components on the logic board.